1. Technical Field
The present invention relates to: an actuator device using piezoelectric elements including a piezoelectric layer whose fluctuations in a polarization direction are suppressed; and a liquid-jet head and a liquid-jet apparatus each including the actuator device as a driving source for ejecting liquid droplets.
2. Related Art
An actuator device including piezoelectric elements caused to displace by application of a voltage is mounted, for example, on a liquid-jet head or the like, which ejects liquid droplets. As a liquid-jet apparatus including the liquid-jet head as described above, there can be cited, for example, an ink-jet recording apparatus including an ink-jet recording head provided with: a plurality of pressure generating chambers which generate pressures for ejecting ink droplets by means of a pressure generation means such as piezoelectric elements, heating elements; a common reservoir which supplies ink to each of the pressure generating chambers; and nozzle orifices communicating with the respective pressure generating chambers. In this ink-jet recording apparatus, ink droplets are ejected from the nozzle orifices when ejection energy is applied on ink in the pressure generating chambers communicating with nozzles that correspond to a printing signal.
The ink-jet recording heads fall into two broad categories: a type having a configuration, as the pressure generation means as described above, where heating elements, such as resistance wires, for generating Joule heat by a driving signal are provided inside the pressure generating chambers, and ink droplets are ejected from nozzle orifices by means of bubbles generated by the heating elements; and a piezoelectric vibration type having a configuration where a part of the pressure generating chamber is configured of a vibrating plate, and by deforming this vibrating plate by means of piezoelectric elements, ink droplets are ejected from nozzle orifices.
Additionally, as ink-jet recording heads of the piezoelectric-vibration type, the following two types have been put to practical use: one using a piezoelectric actuator of a longitudinal vibration mode which causes the piezoelectric elements to extend and contract in an axial direction thereof; and the other using a piezoelectric actuator of a flexural vibration mode.
Here, the piezoelectric element is formed by sequentially laminating a lower electrode, a piezoelectric layer and an upper electrode on a surface of one side of a single crystal silicon substrate. At this occasion, crystallinity of the lower electrode comes to have the same orientation as the plane orientation of the single crystal silicon substrate by receiving influence of the plane orientation of the single crystal silicon substrate which is a base thereunder. Additionally, crystallinity of the piezoelectric layer comes to have the same orientation as the plane orientation of the lower electrode by receiving influence of a base thereunder.
Note that, in practice, on the surface of the one side of the single crystal silicon substrate, an amorphous (non-crystal) layer such as, for example, an oxide silicon layer is before hand provided as abase under the lower electrode. For this reason, the crystallinity of the lower electrode comes to show an orientation having the least energy for crystal growth because it is substantially free from the influence of the crystal orientation of the single crystal silicon substrate. Specifically, when the lower electrode on the amorphous layer is made of, for example, platinum (Pt) and the like, the (111) plane orientation of the substrate is oriented in a direction normal to the single crystal silicon substrate. Then, when the piezoelectric layer is formed on the lower electrode like this, the plane orientation of the piezoelectric layer becomes the (111) orientation.
Additionally, the pressure generating chambers are formed by anisotropically etching a surface of the other side of the single crystal silicon substrate, which is reverse to a surface having the piezoelectric elements. In order to form the pressure generating chambers by thus utilizing anisotropical etching, it is necessary in general to use a single crystal silicon substrate whose plane orientation is the (110) orientation.
However, in order to substantially enhance piezoelectric characteristics of the piezoelectric layer, it is preferable that the plane orientation of the piezoelectric layer should have the (100) orientation when a crystal system thereof is a rhombohedral system. Although, by using the single crystal silicon substrate whose plane orientation is the (110) orientation, an attempt to cause the piezoelectric layer to have the (100) orientation has been made by forming the silicon oxide layer on the surface of one side of the single crystal silicon substrate, and then forming the lower electrode of the (100) orientation on the silicon oxide layer, it has been very difficult to cause the lower electrode to have the (100) orientation.
In response, for example, the following have conventionally been performed: after a lower electrode which is made of platinum, iridium and the like, and which has the (111) orientation, is formed as the lower electrode, titanium (a crystalline type) serving as orientation control of the piezoelectric layer is formed on the lower electrode, and the piezoelectric layer is formed on this titanium. By performing this method, the piezoelectric layer grows freely because presence of titanium as a base causes the piezoelectric layer to be free from the influence of the lower electrode. Therefore, a majority of the plane orientation thereof becomes the (100) orientation. Thereby, the pressure generating chambers can be easily formed by utilizing anisotropical etching, and concurrently a majority of the piezoelectric layer can be oriented in the (100) plane orientation (refer to Patent Document 1).
However, even if titanium serving as orientation control of the piezoelectric layer is provided, the piezoelectric layer is formed through free growth, whereby there exists a problem that the plane orientation thereof cannot be completely the (100) orientation because fluctuations in orientation occur in the piezoelectric layer. Additionally, since strict process management is required in order to form titanium on the lower electrode, manufacturing processes become complicated, whereby there exists a problem that a manufacturing efficiency is low.
Note that, obviously, problems of these kinds occur not only in ink-jet recording heads, but also in other liquid-jet heads.
[Patent Document 1] JP-A-2001-274472 Official Gazette (Scope of claims and other parts)